A rotaxane has a molecular structure consisting of a cyclic molecule, π-conjugated oligomer threaded through the cyclic molecule, and side chains introduced to both ends of the π-conjugated oligomer, wherein the cyclic molecule cannot be pulled out of the π-conjugated oligomer because of the existence of the side chains. A polyrotaxane, which is synthesized by oxidation polymerization of rotaxanes, has characteristics not shared by conventional polymers, and studies have been conducted on polyrotaxanes.
As disclosed in non-patent literatures 1 and 2 and patent literature 1, a conductive polyrotaxane is directly synthesized from an inclusion complex. However, if polymerization reaction should occur the moment the inclusion complex dissociates, repeating units without a cyclic molecule are synthesized within a conductive polymer.
Non-patent literatures 3 and 4 disclose a synthesis method using transition metal ions to form an inclusion complex consisting of a cyclic molecule and a conductive polymer. With this method, however, since a ligand site interacting with transition metal ions must be integrated into the main chain of the conductive polymer, π-conjugation of the conductive polymer is disconnected at the ligand site, which results in decrease in conductivity.
With the formation of an inclusion complex of an electron-accepting cyclic molecule and an electron-releasing oligomer molecule, charge transfer interaction and π-π stacking interaction play an important role to stabilize the inclusion complex. When the oligomer molecule is subjected to oxidation polymerization to form a conductive molecule, the oligomer molecule turns into a radical cation, thus losing electron-releasing property and being made to carry positive charge. Consequently reaction force against the electron-accepting cyclic molecule is generated, which causes the inclusion complex to dissociate. In other words, with the conventional method for obtaining a polyrotaxane based on polymerization of inclusion complexes, repeating units lacking a cyclic molecule is synthesized within the conductive molecule.
Since the equilibrium constant for formation and dissociation of an inclusion complex changes due to a slight difference in conditions such as temperature, solvent concentrations, and the composition of the solution, it is difficult to maintain the quality of conductive polyrotaxanes at a uniform level.